The present invention generally relates to wireless communications networks, and particularly relates to generating and using loop-back signal information from remote receivers, such as mobile stations in a cellular communication network.
Wireless communication typically involves translating information, such as digital data, into a characteristic modulation pattern that is applied to a transmitted carrier signal. A remote receiver obtains the transmitted information by demodulating the received carrier signal. Of course, the transmit-and-receive processes employed in modern digital communication systems involve significantly more complexity, such as the use of sophisticated channel encoding methods for combating signal fade, and error encoding methods for detecting and correcting errors in received data.
Commonly, a receiving device or system improves its reception performance by compensating the received signal for the transmit “channel,” which considers signal corruption effects induced by the transmission medium, and by elements of transmitter and receiver circuits, such pulse shaping filters and signal amplifiers. Such methods base received signal compensation on one or more “channel estimates,” which, in a mobile receiver, are frequently updated to reflect changing propagation path characteristics. Regardless, such channel estimates typically characterize the end-to-end phase and attenuation changes imparted to the transmitted information signal, and may be used to at least partially null or otherwise cancel such effects from the received signal at the receiving system.
An enabling element of such compensation schemes involves the transmission of information known a priori at the receiving device, such as by including a training sequence within a signal transmission that is known in advance to the receiver or by transmitting a known pilot signal in conjunction with an unknown data signal. In either case, the receiver uses the known portion(s) of the received signal(s) to determine its channel estimates. Thus, the receiver estimates the transmission channel between it and the transmitting device.
Of course, advantages may be gained by pre-compensating a transmitted signal for expected channel distortion and/or for expected interference. However, such pre-compensation requires the compensating transmitter to have foreknowledge of the current downlink reception conditions for particular remote receivers. As disclosed in one or more of the parent applications identified above, remote receivers may provide a transmitting system with loop-back signals for use by the transmitting system in estimating the downlink channels between the transmitting system and particular remote receivers. As might be guessed, more accurate channel estimates at the transmitting system enable more effective channel and interference pre-compensation.
However, the use of loop-back signals at the transmitting system, such as for transmit signal pre-compensation at one more downlink signal processing elements within the wireless network, potentially introduces significant signal processing complications. The processing complications and the effectiveness with which the loop-back signals can be used to perform desired transmit signal pre-compensation depends on the methods employed for generating loop-back signals at the particular remote receivers and on the methods used for loop-back processing at the network.